The present invention relates to the field of polymer chemistry and, in particular, to the field of foam composites having properties of both conventional hydrophobic and hydrophilic polyurethane foams.
Conventional polyurethanes have taken a prominent position in the world as an inexpensive material for use in such diverse applications as foam insulation, adhesives, structural foams, shoe sole and others. The properties of conventional polyurethanes that make these uses possible are its physical strength, low cost, ability to make very low density foam, chemical resistance, and thermal stability.
One of the variations of the product family is the manufacture of what are called reticulated foams. These foams are constructed such that the xe2x80x9cwindowsxe2x80x9d that separate the individual cells making up the foam structure are open and the material in the windows collapse into the xe2x80x9cstruts and beamsxe2x80x9d. Thus when fully cured and viewed in a microscope, all one sees is a matrix of xe2x80x9ctinker-toy-likexe2x80x9d rods connected to one another at the ends. One of the advantages of this structure is that it presents very low resistance to the flow of air or water. It is often used as a filter media due to their typically low density and corresponding low cost per unit volume. These foams are hydrophobic, i.e. they do not absorb water.
Hydrophilic polyurethanes, on the other hand, while being of similar chemistry, are used in applications where being compatible with water is the primary reason for their use. These uses include controlled delivery devices, chronic wound care dressings and agricultural media.
An advantage of hydrophilic polyurethanes over conventional reticulated polyurethanes is their ability to be formulated with active ingredients. Hydrophilic polyurethanes are conventionally made by the emulsification and curing of an aqueous phase with a hydrophilic polyurethane prepolymer. The aqueous phase may contain an active ingredient in which case the ingredient is dispersed in the matrix of the resultant foam. In part, it is this ability to incorporate a wide variety of components in the aqueous phase that makes this chemistry commercially attractive.
The essential difference between these two related chemistries is that the hydrophlic polyurethane is compatible with and absorbs water while the conventional polyurethanes are hydrophobic and are incompatible with water. While this hydrophilic nature gives hydrophlic polyurethane its unique applications, it also leads to certain deficiencies. Among these are low physical strength, poor cell size control, relatively high densities causing a relatively high cost per unit volume, and the fact that foam swells considerably upon absorption.
Therefore, although the ability to incorporate certain active ingredients into the hydrophilic polyurethane foams is presently known in the art, this incorporation introduces many adverse characteristics into the foam, limiting the commercial use of hydrophilic polyurethane foams in engineering devices that utilize this technology.
It is an object of the present invention to provide improved foam composites which have properties of both conventional hydrophobic and hydrophilic polyurethane foams.
It is another object of the present invention to provide foam composites which can be used as devices to release active ingredients into a fluid stream.
The present invention which addresses the needs of the prior art provides broadly composite polyurethanes that include both hydrophobic and hydrophilic polyurethane foam entities. By combining these two types of foams, the resulting composite overcomes the disadvantages associated with each, while maintaining their respective advantages.
The composite includes a hydrophobic scaffold foam, such as reticulated polyurethane foam, coated with an open cell hydrophilic polyurethane foam. This is accomplished by coating the inside surface of the reticulated foam with a polyurethane prepolymer emulsion and allowing the composite to cure. What results is a foam composite that uses the reticulated polyurethane foam as a scaffold or a substrate on which the hydrophilic polyurethane foam is cast.
In another aspect of the present invention, the composite foams are formed by contacting a reticulated hydrophobic polyurethane foam with a solution of a hydrophilic polyurethane prepolymer in a solvent such as acetone and the like. The solvent of the polyurethane prepolymer solution is subsequently recovered thus coating the reticulated hydrophobic polyurethane foam with the hydrophilic polyurethane prepolymer.
In another embodiment of the invention the composite foams are provided by contacting the hydrophobic polyurethane foam with a liquid phase of a hydrophilic polyurethane prepolymer at temperatures sufficient to lower the viscosity and thereby control the coating weight of the hydrophilic prepolymer.
It is yet another aspect of the invention to provide a composite that overcomes the disadvantages of both hydrophobic and hydrophilic foams while maintaining their respective advantages. Specifically, the hydrophilic coating, which may or may not contain an active ingredient, provides for the hydrophilic character, while the reticulated foam provides for physical strength and the good flow-through aspects that characterize a reticulated foam. Thus, while the hydrophilic coating will swell when it absorbs water, the reticulated foam is sufficiently strong to prevent an increase in the size of the composite.
It is a further aspect of the invention to provide a composite for use as a device for the controlled release of a component into a stream of fluid passing through it. The stream can be a gas or liquid, but in either case the action of the composite is to release into the stream a component resident in the hydrophilic polyurethane foam coating. Examples include devices for the controlled release of a pharmaceutical to blood, the controlled release of a fragrance to an air stream, the controlled release of a soap to water stream, and the humidification of a gas stream by the evaporation of water from the hydrophilic coating.
It is a further aspect of the invention to provide a composite for use as a device that will chemically or biologically act on the stream that passes through it. The stream can be a gas or liquid, but in either case the action of the composite is to act upon the stream to produce a chemical or compositional change. One example being a device for the bioremediation of a waste stream through the action of bacteria, enzymes, algae, yeasts or other biological species on the waste stream. Another example includes devices that produce an action comparable to those of living cells, such as liver cells, on physiological fluids to remove or react natural or synthetic toxins. Another example includes devices doped or grafted with ion exchange resins for removing complex inorganic ions from the stream. Further examples include devices having foams in doped or grafted with activated carbons or zeolite which have the ability to remove components from a stream by an adsorption or entrapment mechanism. Another example includes devices for the production or removal of chemicals in a process stream through the action of bacteria, enzymes, algae, yeasts or other biological species. Still another example includes devices for the removal of organic species from a process stream by adsorption on the surface of the hydrophilic coating.
Finally, other examples might be the removal of water from a process stream through absorption by the hydrophilic polyurethane foam.
It is a further aspect of the invention to provide a composite for use in devices for the moderation of inhaled air temperatures in low temperature environments. One example of such a device moderates the temperature of inhaled air by passing the air stream over an appropriate phase change material entrapped in the hydrophilic coating. The heat contained in the exhaled air is subsequently trapped by breathing out through another chamber that also contains the phase change material.
It is a still further aspect of the invention to provide a composite for use as an advanced soil-less growing media.
These aspects of the invention are not meant to be exclusive and other features, aspects, and advantages of the present invention will be readily apparent to those of ordinary skill in the art when read in conjunction with the following description, appended claims and accompanying drawings.